Renewable energy sources such as wind energy are an essential tool for reducing the causes of climate change, but wind turbines can pose a collision risk for bats. To date, the population‐level effects of wind‐related mortality have only been estimated for a single bat species. To estimate temporal trends in bat abundance, we considered wind turbines as opportunistic sampling tools for flying bats (analogous to fishing nets), where catch per unit effort (carcass abundance per monitored turbine) is a proxy for aerial abundance of bats, after accounting for seasonal variation in activity. We leveraged a large dataset of standardized bat carcass searches from 594 turbines in southern Ontario, Canada, correcting for surveyor efficiency and scavenger removal. We used Bayesian hierarchical models to estimate temporal trends in aerial abundance of bats and explore the effect of spatial factors (including landscape features associated with bat habitat, such as wetlands, croplands and forested lands) on the number of mortalities for each species. We found strong evidence of rapid declines in the abundance of four species in our study areas, with declines in “capture” of carcasses over seven years ranging from 65% (big brown bat) to 91% (silver‐haired bat). Estimated declines were independent of the effects of mitigation (increasing turbine cut‐in speed from 3.5 to 5.5 m/s), which significantly reduced but did not eliminate bat mortality. Late‐summer mortality of hoary, eastern red, and silver‐haired bats was predicted by woodlot cover, while mortality of big brown bats decreased with increasing elevation. These landscape predictors of bat mortality can inform the siting of future wind energy operations. Nevertheless, our most important result is the apparent decline in abundance of four “common” species of bat in the airspace, which requires further investigation.